Hydrogels are three-dimensional polymer networks, and these networks can be formed by chemical cross-linking of monomers or self-assembly of monomers through non-covalent interactions (1). All naturally occurring biomolecules except RNA are known capable of forming hydrogels (2, 3). The other type of nucleic acids, DNA, can readily form hydrogels since double-stranded DNA with compatible sticky ends can be designed to form hydrogel networks by self-assembly. In contrast, RNAs are generally single stranded, form intra-strand double helixes, and adopt complex tertiary structures, through Watson-Crick base paring (guanine-cytosine or G-C and adenine-uracil or A-U), noncanonical base pairing (e.g., G-U or A-A) and complex tertiary interactions, such as base stacking, kissing loops and pseudoknots (4, 5). As such, RNAs have been shown to act in additional roles as catalysts (6), aptamers (7) and riboswitches (8). However, RNA has not been reported to form a molecular network, resulting in a hydrogel, presumably because no RNA has been shown to possess “sticky ends” and/or modular sequence segments as designer building blocks for network assembly through intermolecular interactions.